Chapter 2. Liquid Phase Reactive Sintering of a Complex WCoB-TiC Cermet

Summary

The WCoB is a complex boride that has a very high hardness (45 GPa). In previous works, a very fine coating with a high percentage of this compound has been obtained as a product of surface reaction of pre-sintered samples of WC-Co and WC-Co-TiC with TiB₂ or other compounds rich in boron, at 1100d̀C in vacuum. The aim of this work was to promote the formation of the WCoB as a second phase in a bulk by liquid phase reactive sintering of equimolar mixtures of WC and TiB₂ with Co varying between 10 - 47 wt%, in order to evaluate its influence on the sintering and formation of WCoB. Sintering was performed in the temperature range: 1400–1600d̀C. The sintered samples were evaluated using SEM, EDX, XRD, EPMA and XPS analyses. It was found that the alloy showing the best properties was that with 18wt% of cobalt which corresponded to a nominal equimolar mixture of WC, TiB₂ and Co. The sintered microstructure consisted primarily of WCoB, TiC and some minor quantities of CoB and W₂CoB₂. A relation between initial Co contents, volume fraction of the different phases formed and mechanical properties is presented.